This work is directed at the development of a microelectrode array for electrocorticography (ECoG) that allows the recording and stimulation of neural activity on the surface of the brain over a large area at high spatial resolution. Existig technologies either allow the recording of neural activity (i) over a large brain area at low spatil resolution (standard commercial ECoGs), or (ii) over a small brain area at high spatial resolution (so called ECoGs). BMSEED aims to produce large-area-high-resolution ECoG electrode arrays (lahrECoGs). Conventional ECoG electrode arrays are placed on the surface of the brain, and are used as a less invasive alternative to penetrating microelectrodes, which are inserted into the brain tissue. They are used (i) in neuroscience research to explore the fundamentals of how the brain operates, (ii) in brain-machine-interfaces (BMIs) to record neural activity to drive a neuroprosthesis for amputees or to move a computer cursor for the paralyzed, and (iii) for monitoring neural activity during epilepsy surgery to identify the regions of the corex that generate seizures, which subsequently are removed. These applications would benefit from BMSEED's lahrECoG because it would provide more accurate localization of the recorded signals (i.e., normal neural activity as well as seizures) over a large area, thus improving brain research, making BMIs more robust, and improving clinical outcomes in epilepsy surgery by providing the neurosurgeon with more accurate localization of seizure activity. In all ECOGs, each recording electrode requires one wire to electrically connect to the data acquisition system without intersecting (i.e., without shorting) with other wires. This becomes increasingly difficult as the density and total number of electrodes increases. BMSEED's lahrECoG solves this problem by routing the lead wires on multiple levels. In addition, our proprietary technology to produce mechanically robust microelectrodes using microfabrication techniques allows us to reduce the thickness, thus the stiffness, of the device, making the implant more compliant. Importantly, BMSEED's lahrECoG consists entirely of materials that are suitable for implantation in humans, thus simplifying the FDA approval process. The first specific aim is to optimize the profile of the slope between different levels to provide a reliable electrical connection, and to fabricate and electromechanically characterize prototypes of the lahrECoG. The second aim is to demonstrate the biocompatibility and capabilities of the prototypes. To that end, a lahrECoG will be chronically implanted in five cats, and neural recording and micro-stimulation data will be obtained for at least two months. At the end of phase I, BMSEED will have (i) developed the capability to produce multi-level metallization and prototypes of lahrECoGs, and (ii) characterized their capabilities in a cat model. In phase II, BMSEED will extend the lahrECoGs development to multi-level metallization on larger, clinically relevant substrate sizes. Our customers will initially be research laboratories, and, after FDA approval, biomedical companies for BMI applications and hospitals for clinical applications.